Furnace



April 20, 1937. a. HARTER ET AL FURNACE Original Filed Feb. 20, 1932 3 Sheets-Sheec l INVENTOR Isaac Harier B Perry 1?. Ca Sidr ATTORNEY APFYEH 1937- I. HARTER ET AL 2,077,410

FURNACE Original Filed Feb. 20, 1952 3 Sheets-Sheet 2 INVENTORS Isaac Harfef BY Perl 1?. Cass/Hy.

ATTORNEY.

Aprifi 1937- a. HARTER ET AL 2,077,410

FURNACE Original Filed Feb. 20, 1932 3 Sheets-Sheet 3 W a! g 1 ii w 4 42 WWI 42 ml? P M W INVENTOR Isaac Hd/f'er Parr lPlCas/a B 5 y ATTORNEY Patented Apr. 20, 1937 UNITED STATES PATENT OFFICE FURNACE SBY Application February 20, 1932, Serial No. 594,200 Renewed January 4, 1936 10 Claims.

This invention is concerned with improvements in furnaces. It specifically relates to fluid cooled types of walls for high capacity furnaces for vapor generators.

The invention involves improvements providing flexible arrangements of wall elements which are inherently capable of operative mutation to give desirably different degrees of wall protection and heat absorption from the furnace gases.

The invention provides constructions adjustable to a wide variety of fuels and furnace conditions, and particularly to slag forming fuels having a wide range of ash fusing and melting temperatures and ash content in relation to the combustible.

Most of the fluid cooled furnace walls in use consist of spaced tubes preferably vertical with tile, blocks of metal or refractory, or brick work,

interposed or exteriorly positioned on the furnace,

20 side. In some cases bare metal is exposed. It is important, from the standpoint ofproviding adequate ligament strength in the connected headers and from the standpoint of low insta1lation cost, that such tubes have a wide spacing.

However, in known installations, such spacing exposes the interposed tile to the destructive action of molten ash or slag acting in a fluxing manner to wash away refractory. It is an object of this invention to prevent the occurrence of this action to an excessive degree when it is necessary to screen the metal to secure desired wall face and furnace temperatures higher than is possible with bare tubes or plates cooled on their opposite sides.

It has been proposed, in other types of water cooled walls, to provide bare metallic closure means for the spaces between the tubes. Such constructions give a higher temperature of wall face than the bare tubes but involve excessive installation costs and some difficulties about tube spacing in relation to the maintenance of good thermal contact between the tubes and metal as well as other difficulties of localized expansion stresses. A further object of the present invention is to overcome such difliculties.

Another object of the invention is to provide structures involving such adequate heat absorption in the intertube spaces that the refractory or 50 insulating backing is protected without affording a degree of absorption so high that wall face temperatures are unduly lowered. At the same time there is provided a protective covering for the tube face itself to the same end. More par- 55 ticularly, there is provided a permanent refractory heat insulation shield between the source of heat and the tubes. This is done in a manner which is highly adaptable to different furnace conditions.

By different combinations of tubes, studs welded to the tubes, and refractory, all correlated to meet the requirements of adequate combustion and boiler operation under desired furnace conditions, the present invention presents improved furnace structures. Heat absorption may be kept low and wall temperature may be kept high in some zones, as for example, at the points adjacent furnace slag pools, and simultaneously, heat absorption can be kept at a high rate and wall temperature low at other zones where, for example, it is desired to generate steam in the wall tubes and to chill the furnace gases before they enter the boiler tube bank.

Combinations illustrative of the invention are shown in the accompanying drawings, in which:

Fig. 1 is a diagrammatic view in the nature of a vertical section of the illustrative furnace associated with a steam generator.

Fig. 2 is a fragmentary sectional view through a portion of a wall for such a furnace as that illustrated in Fig. 1.

Fig. 3 is a fragmentary front elevation of a studded tube showing that tube without any refractory between the studs.

Fig. 4 is a side elevation of the structure illustrated in Fig. 3.

fled tube construction.

Fig. 6 is a transverse section of a tube having rows of studs in staggered arrangement.

Fig. 7 is a fragmentary sectional view through a portion of a furnace wall similar to the wall indicated in Fig. 2.

Fig. 8 is a fragmentary elevation of a section of a furnace wall having parts of refractory layers removed to indicate the arrangement of studs on the tubes and also illustrating two different temperature zones resulting from different use of studs and refractory in the upper and lower parts of the furnace.

Fig. 9 is a fragmentaryhorizontal section taken on the line 9-9 of Fig. 8 and indicating the tubes as bare in a furnace zone of higher temperature.

Fig. 10 is partly an elevation and partly a section taken at right angles to Fig. 8.

Fig. 11 is a. fragmentary sectional view taken along the line l|-|l of Fig. 8.

Fig. 12 is a fragmentary sectional view through a portion of a modified furnace wall having headed studs welded to its fluid conducting tubes.

In the drawings, Fig. 2 indicates a row of wall cooling tubes l0 having an insulating stratum l4 interposed and extending over the tube sides away from the furnace gases. When this stratum is not held in place by a furnace casing or an outside brick wall, tension members I I may be provided. They are preferably welded to the tubes l0. Bridge pieces l3 contact with the outside of this stratum.

Toward the furnace, studs l2 are secured to the tubes by welding. Heat is thereby rapidly conducted into the tubes without overheating of the stud ends nearest the furnace gases, and conse-- quently the temperature of the studs is kept properly low.

The studs nearest the insulation l4 and projecting partly across the intertube spaces intercept the heat that would otherwise be transmitted to the insulation. This intercepted heat is conducted directly to the metal walls of the tubes I0. In this manner the studs act to keep wall temperatures within desirable limits. When the high temperature refractory i5 is provided the studs also act as anchors to hold the refractory in operative position.

Effectively rapid heat transfer from the furnace ends of the studs to the tubes is enhanced when the studs have such heads as are indicated at H in Fig. 2. These headed studs provide wide bases fused into the tube metal. Shoulders are also thereby provided to enhance the welding operation. Pressure against these shoulders and electrical welding contact therewith tend to promote economy of manufacture of the illustrative structure. Overheating of the studs is also prevented.

If in electrically welding studs to the tubes pressure and current were to be applied at the ends of the studs remote from the tubes, there would be danger of overheating of the studs. To overcome this the present invention involves the application of the pressure and current to shoulders or heads on the studs near their ends which are in contact with the tubes. When the headed studs of such structures as those indicated in Figs. 3, 4, 5, and 6 are welded to the tubes in staggered positions in adjacent rows there is more efiective interlocking and anchoring of the refractory 44 between the tubes. The number of studs in a plurality of adjacent rows thereby approaches a maximum for zones confined to the confronting sides of adjacent tubes in the same row.

Studs exposed to the intense radiant heat and the slagging action of a modern boiler furnace would have their ends burned away if they were too long. Other considerations also operate to determine stud lengths. If the studs extending into the intertube spaces are too short thetube spacing will be too small to permit the desired interception of radiant heat between the tubes. Such an organization would involve excessively high installation costs due to the large number of tubes. It would also involve an undesirable reduction of the ligament strength in the headers in which the tubes are expanded. Accordingly, this invention provides a wide tube spacing with the studs 20 in the intertube spaces longer than the front studs l8 shown in Figs. 8, 11 and 12.

When the furnace temperatures become excessively high, the face of the refractory layer will melt away. This action will continue until the cooling action of the studs has a counter-acting effect. The wall fluxing action will then be checked. The interplay of these actions results in slag deposits when the cooling effect predominates. The wall then builds up until the furnace temperature again becomes excessive when melting away begins. The latter may result in the burning away of the ends of the studs when the latter are too long.

When, as shown in Figs. 8, l1 and 12, the studs across the front or furnace faces of the tubes are short and covered with refractory, a temperature equilibrium is maintained by the interplay of the actions above mentioned. Here, there will be no substantial burning away of the front studs .even under furnace conditions which involve an intense heat and an excessively destructive tendency by the molten slag formed during the combustion of the fuel. The shorter studs H! are not exposed directly and the longer studs in the intertube spaces are not so severely heated.

In furnace zones beyond the combustion zone and near the boiler of the illustrated organization it is desirable to cool the furnace gases in order that the maximum of slag particles suspended in the products of combustion may be caused to deposit before they can contact with the main bank of steam generating tubes. Accordingly this invention provides a furnace wall having higher heat conductivity rates. Such a structure is illustrated in the upper parts of Figures 8 and 10. Here, the tube portions 42' are bare across their inner or furnace faces. The short studs intermediate the dual rows of staggered side studs 20 are eliminated, but the intertube spaces are closed by refractory portions anchored by the embedded staggered studs.

The higher temperature furnace zone, or combustion zone structure, is illustrated at the lower parts of Figures 8 and 10. Here the studs are preferably distributed entirely across the furnace sides of the tubes, with the short front studs l8 arranged between the long inter-tube studs 20. All of the studs and the front faces of the tubes are preferably covered by the refractory layers 46 as indicated.

Fig. 10 indicates a sectional view of the wall shown in Fig. 8. Here a refractory layer 28 is backed by an outer wall layer 48 just inside the furnace casing 50.

In the maintenance of thermal equilibrium atthe inner faces of the illustrative walls, there occurs a thinning down of the refractory. At positions where the studs then exert their cooling effects slag is subsequently built up, with the inner wall layer always maintained at fusing temperature. These actions result in an uneven and wavy wall surface, promoting a greater degree of slag deposit from the burning fuel. This means a quicker recovery from a thinned down wall condition when furnace temperatures change. The illustrative structures produce these results with considerable economy of installation and repair costs.

The present invention involves the repair or alteration of existing furnaces by the welding of the illustrative studs to the tubes in these furnaces.

The above indicated alteration can be carried out in furnaces having displaced tubes. Even though adjacent tubes of such furnaces are badly distorted, a complete furnace wall can be made in accordance with the teachings of this invention.

In Figures 3 and 4 the furnace face of the tubes 29 is shown as having transverse projections 30 which may be integrally formed, as in rolling the tubes. These projections are preferably arranged in a row located between the opposite rows of staggered studs 22. When such tubes are exposed as bare tubes to the .heat of slag forming fuels, slag or fused ash may accumulate on the projections.

The above described furnace constructions are applicable to such an installation as that shown in Fig. 1. Here, there is a large furnace installed underneath a steam boiler. The furnace is provided with means for burning a slag producing fuel in the combustion chamber 52. The burner 54 shown is for pulverized coal.- It has its discharge outlet between wall tubes 56 which are shown connecting the upper header 58 to the lower header 60. These headers are connected outside the furnace by circulation tubes 62. Up-

take tubes 64 connect the header 58 with the steam and water drum 66 of the boiler.

Along the opposite wall of the furnace are water cooled tubes 68 connecting the upper header 10 with a lower header [2. Outside circulation tubes connect these headers, and the upper header is connected into boiler circulation-by such means as the tube 16.

The illustrative furnace is a slag tap furnace having means 18 provided at its bottom for the withdrawal of slag therefrom. Above the furnace is located a steam boiler having horizontally inclined steam generating tubes 80 connecting an uptake header 82 with a downtake header 84. The latter is connected to the steam and water drum 66 by nipples 86 which extend across the gas pass leading to the flue 88. Uptake tubes 90 lead to the steam circulator portions 92 which are shown as located above a superheater 94.

In the illustrative combination the diameters, lengths, and spacings of the studs are so proportioned that substantially all of the refractory between the studs is maintained at temperatures below the fusion point of the refractory or below the temperature at which slag erosion occurs. The interposed refractory is also maintained at a temperature below the temperature at which slag reaction occurs. The temperatures of the hottest parts of the studs are below the temperatures at which progressive oxidation occurs.

While the invention has been described with particular reference tb the structures shown in the drawings, it is to be appreciated that it is not limited thereto but is of a scope commensurate with the scope of the sub-j0ined claims.

It is also to be understood that the different drawings illustrate parts of the invention which may be used in conjunction with .the construction shown in the figures of the drawings. For instance, the intertube studs of the Fig. 2 wall may be arranged in the manner indicated in Fig. 6 of the drawings. Also, the ribs shown in Figs. 3 and 4 may be eliminated from the combination of these figures and such short studs as those indicated in Fig. 11, or Fig. 12, used in lieu thereof. Again, and with reference to the Fig. 12 wall construction, the intertube studs may be longer, and may be arranged in two rows as are the studs of the Fig. 6 structure. Similarly, it is 65 within the purview of the invention that the Fig. '7 structure may be modified by combining such arrangement of studs as those indicated in Figs. 6, 11 and 12 of the drawings. The invention is not to be taken as limited to any one of the wall constructions exactly as it happens to be shown in one particular figure of the drawings.

What is claimed is:

1. In a boiler furnace wall, a row of spaced wall cooling tubes, diametrically opposed rows of staggered headed metallic studs welded to the tubes in the plane of the wall and disposed between adjacent tubes, and projections between said rows so as to present an uneven surface on the face of the tube exposed to the furnace heat and the slag deposited from burning gases in the furnace.

2. In a boiler furnace, a row of fluid conducting wall tubes, rows of long headed studs disposed in staggered arrangement along diametrically opposed positions on the tubes in the plane of the wall, and short studs welded on the furnace faces of the tubes between the opposed rows of studs.

3. In a furnace, a row of spaced wall cooling tubes, headed studs, and refractory positioned as a plastic between the studs and the tubes, the studs being welded to the facing sides of adjacent tubes with their headed ends at the tubes and their opposite ends about midway of the refractory between successive tubes.

4. In a furnace, spaced wall tubes, long intertube headed studs extending from the facing sides of adjacent tubes to positions approximately midway of the spaces between the tubes and welded to the tubes in staggered arrangement in adjoining rows, shorter headed studs distributed over the furnace faces of the tubes between the opposite rows of inter-tube studs, refractory over tubes adjacent all of the studs, fuel burning means, and means for connecting the tubes into a fluid circulation, all of the studs extending outwardly from the tubes and welded thereto with their heads at their tube ends united with the metal of the tubes, the heads of all of the studs having a greater cross section than their main portions.

5. In a fluid heat exchange device, a furnace, means for burning fuel in the furnace, and tubular furnace wall structures of different conductivity capacities in succeeding zones of different temperatures; said last named structures operating to effect a control of furnace temperatures and including spaced wall tubes, means connecting the tubes into fluid circulation; headed metallic studs welded to the tubes with their heads contacting the tubes, and refractory associated with the tubes and the studs so as to control the fluid heat absorption in correspondence with the different temperatures in the different zones of the furnace, the refractory and studs covering the furnace sides of the tubes in a high temperature zone of the furnace while in a zone of lower temperature the studs and associated refractory cover only opposite portions of the tubes in line with the wall so as to leave the intermediate tube faces bare.

6. In a tubular heat exchanger adapted as a part of the furnace wall to transmit to a contained fluid the heat received radiantly from fuel burning in the furnace; said tubular heat exchanger having a row of tubes constituting a metallic inner part in contact with the contained fluid; and

a composite outer structure exposed to radiant heat from the burning fuel; said outer structure comprising metallic projections extending outwardly from the inner part and rigidly connected therewith, with the projections on at least some of the tubes independent of the projections on others of the tubes, and refractory material contacting with the inner part and located between the projections, said refractory material being of greater thermal resistance than the material of the remaining structure thereby preventing overheating of the exchanger metal and contributing to higher furnace temperatures; saidmetallic projections including rows of long metallic studs projecting outwardly from the facing sides of adjoining tubes, and shorter studs welded to the tubes between the rows of long studs and distributed over the furnace faces of the tubes, both the long and short studs being of the same type.

7. In fluid heat exchange apparatus, a furnace including a wall having spaced cooling tubes connected into fluid circulation, fuel burning means, relatively long metallic studs welded to the tubes and projecting therefrom into the intertube spaces, shorter metallic studs welded to the tubes and positioned between said rows of long studs, and heat resisting refractory material installed as a plastic between the studs and the tubes, some of said studs being headed at their tube ends.

8. In fluid heat exchange apparatus, a furnace wall including spaced tubes connected into a fluid circulation, a plurality of closely spaced rows of metallic studs on each of two opposite sides of the individual tubes, said sides facing the intertube spaces, and non-metallic refractory material positioned as a plastic between the tubes and around the studs to complete the furnace wall, the studs of adjoining rows on each side of a tube being outwardly divergent with respect to the center of the tube and arranged in staggered formation so as to form an advantageous anchorage for the refractory material and the refractory covering all of the studs between tubes so that a high temperature furnace face is presented at those positions.

9. In a tubular heat exchanger adapted as a part of a furnace wall to transmit to a contained fluid the heat received radiantly from fuel burning in the furnace; said tubular heat exchanger including a row of wall tubes constituting metal- 40 he inner parts in contact with the contained fluid;

and composite outer structures exposed to radiant heat from the burning fuel; said outer structures comprising metallic studs extending outwardly from the inner parts and having widened and 45 enlarged heads at their ends next to the tubes fused into the metal of the tubes by welding, with inter-tube studs projecting from adjacent tubes to positions substantially midway of the intertube spaces and'with'the inter-tube studs on at least some of the tubes independent of the studs on others of the tubes, and ceramic refractory material installed as a semi-plastic in contact with the inner parts and between the headed studs to form furnace face portions protecting the inter-tube studs, said refractory material being of greater thermal resistance than the material of the remaining structure to thereby prevent overheating of the exchanger metal and contributing by incandescent furnace faces to higher furnace temperatures; the enlarged tube end heads of the studs having cross sections of greater area than the remaining parts of the studs to effect higher rates of heat transfer and enhance the welding operation.

10. In a tubular heat exchanger adapted as a part of a furnace to transmit to a contained fluid the heat received radiantly from fuel burning in the furnace; said exchanger including spaced tubes, each constituting a metallic inner part in contact with the contained fluid; and a composite outer structure exposed to radiant heat from the burning fuel; said outer structure comprising metallic studs extending outwardly from each inner part and having widened and enlarged heads at their respective tube ends fused into the metal of the tubes, with the studs arranged in rows spaced along each tube and extending in substantially opposite directions toward adjacent tubes, and ceramic material installed as a semiplastic in contact with the inner parts and between the studs to form furnace face portions protecting the studs, said refractory material being of greater thermal resistance than the ma-- terial of the remaining structure to thereby prevent overheating of the exchanger metal and contributing to higher furnace temperatures; the stud heads having cross sections of greater area than the remaining stud parts which are of uniform cross section where they extend into the refractory material and anchor it on the tubes; the stud heads being enlarged to effect higher rates of heat transfer and to afford shoulders to which the welding pressure is applied at positions close to the tubes.

ISAAC HARTER. PERRY R. CASSIDY. 

